1. Field of the Invention
The present invention relates to a vibration motor, and more particularly, to an improved vibration motor which can minimize mechanical friction and electric spark between brushes for receiving electric current and a commutator arranged in a rotor in order to prolong the lifetime of the motor as well as to enhance the reliability thereof.
2. Description of the Related Art
As well known in the art, a communication device generally uses a bell and a vibrator to inform a user of call incoming. A vibration mode typically actuates a small-sized vibration motor transferring driving force into a housing of the communication device to vibrate the communication device.
The vibration motor currently applied to a mobile telephone is discriminated into a flat type vibration motor (or coin type vibration motor) and a cylinder type vibration motor. The flat type vibration motor has a relatively simple vibration structure, e.g., of rotating a weight of high specific gravity which is placed inside the motor. The flat type vibration can be fabricated thin so that components of a mobile phone can be readily miniaturized. Owing to these advantages, application of the flat type vibration motor is gradually spreading.
FIG. 1 is a sectional view of a conventional flat type vibration motor, and FIGS. 2A and 2B are plan and bottom views of a rotor of the flat type vibration motor. As shown in FIGS. 1 through 2B, the conventional flat type vibration motor 300 generally comprises a stator assembly 100 functioning as a stationary member (hereinafter will be referred to as xe2x80x9cstatorxe2x80x9d) and a rotor assembly 200 functioning as a rotary member (hereinafter will be referred to as xe2x80x9crotorxe2x80x9d).
The stator 100 includes a disk-like lower plate 110 having a cylindrical shaft holder 115 projected to a predetermined height from an upper central portion of the lower plate 110 for fixing the lower end of a shaft 140 via insert press. The stator 100 also includes a lower board 120 which is integrally attached to the upper face of the lower plate 110 and on which a circuit pattern is printed. A terminal unit 125 is mounted on a distal portion of the lower board 120 and connected with an external power supply (not shown).
An annular magnet 130 is mounted on the upper outer periphery of the lower plate 110, and has N and S poles in the outer periphery of the magnet 130 which are alternatingly magnetized to an equal interval.
The stator 100 also includes a pair of brushes 160 spaced from each other at a predetermined angle and arranged adjacent to an upper central portion of the lower board 120. Each of the brushes 160 is electrically connected with each of input and output terminals of the terminal unit 125.
A cylindrical housing 150 is coupled from above with the outer periphery of the lower plate 110 in order to protect the stator 100 and the rotor 200. A shaft hole 155 is formed in a central portion of the underside of the housing 150 to axially support the upper end of the shaft 140.
The rotor 200 is arranged rotatable about the stator 100 via the bearing member 145 of the shaft 140, and includes an upper plate 210, a commutator 220, a weight 230 and a pair of winding coils 240.
The upper plate 210 is arranged in the underside of an insulator 250, and the weight 230 and the winding coil 240 are integrally contained within the insulator 250 via insert injection molding. The commutator 220 has a number of segments which are buried in the underside of the upper board 210 around the center of rotation at a predetermined interval, exposing contact faces thereof. The segments are electrically connected with the upper ends of the brushes 160 through elastic contact.
The weight 230 is arranged between the winding coils 240 in order to maximize eccentricity in actuation of the motor, and made of high specific gravity material such as tungsten.
The winding coils 240 are opposed to each other on a common radius of rotation which is substantially equal to that of the magnet 130 placed under the winding coils 240. One of the winding coils 240 is supplied with electric current of a polarity, which is different from that of the other one of the winding coils 240 by the commutator 220 in contact with the brushes 160.
In the conventional vibration motor 300 of the above construction, when the lower plate 120 is supplied with electric current from the external power supply via the terminal unit 125, electric current is introduced into the commutator 220, which is arranged in the upper board 210 in elastic contact with the upper ends of the brushes 160, via the brushes 160 having lower ends electrically connected with the lower plate 120. Then, electric current is supplied from the commutator 220 via the circuit pattern printed on the upper board 210 into the winding coils 240.
In this case, magnetic fields created from the winding coils 240 and the magnet 130 interact with each other to generate electromagnetic force thereby rotating the rotor 200 in a direction. The commutator 220 periodically alternates the polarity of electric current supplied to the winding coils 240 as the winding coils 240 of the rotor 200 relatively change positions in respect to the magnet of the stator 100.
The rotor 200 having the weight 230 arranged eccentrically therein is rotated eccentrically in one direction around the shaft 140 as the center of rotation. Eccentric rotation of the rotor 200 is transferred via the shaft 140 to the lower plate 110 and the housing 150 to create vibration so that the vibration motor 300 can be used as a silent call device of a mobile communication device.
However, the above conventional vibration motor 300 has drawbacks that the brushes 160 cause mechanical abrasion or generate electric spark while passing through gaps G of the segments of the commutator 220 during rotation of the rotor 200. Then, byproducts such as black powder may be created to deteriorate the stability of electric contacts between the brushes 160 and the commutator 220, functioning as a major factor of degrading the performance of the vibration motor as well as creating noise. Such problems also resultantly shorten the lifetime of the vibration motor.
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide an improved flat type vibration motor which can minimize mechanical friction and electric spark from brushes for conducting electric current between a stator and a rotor in order to prolong the lifetime of the motor as well as to prevent deterioration of motor performance thereby enhancing the reliability of an article.
According to an aspect of the invention for realizing the above objects, there is provided a flat type vibration motor for generating vibration in energization. The flat type vibration motor comprises: a stator including a lower board with a terminal unit, the terminal unit being supplied with electric current from an external power supply, and a magnet having N and S poles alternatingly magnetized in a periphery of the magnet; a shaft having a lower end fixedly pressed into an upper central portion of the stator and an upper end assembled into a lower central portion of a housing; a rotor rotatably assembled between the stator and the housing, wherein the rotor includes an insulator of eccentric mass, which integrally contains at least one winding coil corresponding to the magnet and a weight arranged eccentrically adjacent to the winding coil, and an upper board mounted on an underside of the insulator; a plurality of brushes electrically connected with the terminal unit and having lower ends fixed to the stator; a plurality of annular slip rings arranged in an underside of the upper board to have an axis concentric with the shaft, each of the rings contacting an upper end of each of the brushes; and an Integrated Circuit (IC) chip for converting the direction of electric current flowing through the winding coil by alternating the polarity of electric current which is introduced to the slip rings via the brushes and then supplied to the winding coil.
It is preferred that the brushes include a negative pole brush and a positive pole brush divided from the negative pole brush, the positive pole brush having a length different from that of the negative pole brush.
It is preferred that the upper ends of the brushes are inclined and placed over a top of the magnet.
It is preferred that the slip rings include a negative slip ring and a positive slip ring, the positive slip ring having an outside diameter different from that of the negative slip ring not to overlap with the positive slip ring.
It is preferred that each of the slip rings has an underside contacting the upper end of the each brush, wherein the underside is formed of a smooth flat face continued along a periphery of the each slip ring and having uniform surface roughness.
It is preferred that the IC chip is arranged in the upper board having a circuit pattern for electrically connecting the slip rings with the winding coil.
It is preferred that the slip rings and the brushes form at least one electric contact.
According to another aspect of the invention for realizing the above objects, there is provided a flat type vibration motor for generating vibration in energization, comprising: a housing; a shaft having an upper end supported to the housing; a rotor rotatably arranged within the housing, and including at least one winding coil, a weight eccentrically arranged adjacent to the winding-coil and a plurality of annular slip rings arranged in an underside of an upper base; an Integrated Circuit (IC) chip arranged in an upper face of the upper base for converting the direction of current flowing through the winding coil; a stator having a magnet arranged in a lower base thereof, the magnet having N and S poles alternatingly magnetized in an outer periphery thereof; and a plurality of brushes having one ends correspondingly contacted with the slip rings and the other ends electrically connected with a terminal unit which is supplied with electric current.
It is preferred that the upper base comprises a printed circuit board having a circuit pattern formed in an upper face of the printed circuit board to electrically connect the slip rings with the winding coil, wherein the IC chip is arranged in the upper face of the printed circuit board.
It is preferred that each of the slip rings comprises an annular conductive metal member which is attached to the underside of the upper base and arranged concentric with the shaft.
It is preferred that each of the slip rings comprises an annular conductive pattern which is printed on the underside of the upper base and arranged concentric with the shaft.
It is preferred that the slip rings comprise a negative slip ring and a positive slip ring, the positive slip ring having an outside diameter different from that of the negative slip ring not to overlap with the positive slip ring.
It is preferred that the brushes include a negative pole brush and a positive pole brush divided from the negative pole brush, the positive pole brush having a length different from that of the negative pole brush.
It is preferred that the upper ends of the brushes are inclined and placed over a top of the magnet.
It is preferred that each of the slip rings has an underside contacting the upper end of the each brush, wherein the underside is formed of a smooth flat face continued along a periphery of the each slip ring and having uniform surface roughness.
It is preferred that the slip rings and the brushes form at least one electric contact.
It is preferred that the lower base comprises a lower board having a circuit pattern formed on an upper face thereof for connecting the terminal unit with the brushes.
It is also preferred that the rotor further includes an insulator of eccentric mass integrally having a weight therein, the weight being eccentrically arranged adjacent to the winding coil.